1. Field of the Invention
The present invention relates to a measurement apparatus and a measurement method. More particularly, the invention relates to a measurement apparatus for measuring the dimensions of the outer configuration of a surface mounted-type semiconductor device and a method of measuring the same.
2. Description of the Related Art
FIG. 33 is a schematic view illustrative of the construction of a lead flatness measurement apparatus for a conventional semiconductor device by way of example. FIG. 33 shows a semiconductor device 1, a package 1a for the semiconductor device 1, leads 2 of the semiconductor device 1, end surfaces 2a of the leads 2, a mounting base 3 for having the semiconductor device 1 mounted thereon, a pit 3a of the mounting base 3, a transparent mounting plate 4 fit into the mounting base 3 so as to have the semiconductor device 1 mounted thereon, a light-shielding band pattern 4a on the transparent mounting plate 4, a drive electric motor 5 for rotating the mounting base 3, a belt 5a connecting the mounting base 3 and the electric motor 5, and first and second illumination units 6A and 6B for illuminating the semiconductor device 1 from below through the transparent mounting plate 4.
FIG. 33 further shows: a first imaging device 7a for forming an image of the semiconductor device 1 and the light-shielding band pattern 4a from respective angles of elevation; a second imaging device 7b for forming an image of the semiconductor device 1 and the light-shielding band pattern 4b from different angles of elevation from those of the first imaging device 7a; first and second image information items 8a and 8b which are output from the first and second imaging devices 7a and 7b, respectively; first and second lead-end distance detection means 9a and 9b for receiving the first and second image information items 8a and 8b, respectively; first and second distance information items 10a and 10b which are output from the first and second lead-end distance detection means 9a and 9b, respectively; lead height detection means 11 for detecting the height from the bottom surface of each of the leads so as to receive the first and second distance information items 10a and 10b; lead height information 12 which is output from the lead height detection means 11; a storage device 13 including divided components 13a-13d for storing the lead height information 12 therein; lead height information 14 which is output from the storage device 13; and lead flatness detection means 15 for receiving the lead height information 14.
A description will now be given of the operation of the conventional lead flatness measurement apparatus constructed as described above. The surface mounted-type semiconductor device 1 is constructed such that a plurality of leads 2 projects downward from each lateral surface of the package 1a formed of a sealing resin, the forward end of each lead 2 being horizontally bent outward. The mounting base 3 is rotatably supported by supporting means (not shown). The light-shielding band pattern 4a is formed on the top surface of the transparent mounting plate 4 which is fit into the pit 3a of the mounting base 3 so as to opposedly face, across a predetermined distance, the end surfaces 2a of the leads 2 on each lateral surface of the semiconductor device 1.
The drive electric motor 5 gradually rotates the mounting base 3 by 90.degree. via the belt 5a. Further, the first illumination unit 6A is placed to apply light downward that is reflected upward from the end surfaces 2a of the leads 2 arranged on one lateral surface of the semiconductor device 1, while the second illumination unit 6B is placed to apply light to the end surfaces 2a of the leads 2 in an obliquely upward direction. The first imaging device 7a is placed above the first illumination unit 6A so as to forming an image of the end surfaces 2a of the leads 2 and to output the image information item 8a to the first lead-end distance detection means 9a. On the other hand, the second imaging device 7b is placed in an obliquely upward direction of the second illumination unit 6B so as to forming an image of the end surfaces 2a of the leads 2 and to output the image information item 8b to the second lead-end distance detection means 9b.
The first lead-end distance detection means 9a detects the distance between the end surface 2a of the lead 2 and the light-shielding band pattern 4a according to the image information item 8a. The second lead-end distance detection means 9b detects the distance between the end surface 2a of the lead 2 and the light-shielding band pattern 4a according to the image information item 8b. The first and second distance information items 10a and 10b are input into the lead height detection means 11 from the first and second lead-end distance detection means 9a and 9b, respectively, so that the lead height detection means 11 can detect the height from the bottom surface of the lead 2 and the transparent mounting plate 4. The lead height information 12 is input into the storage device 13 from the lead height detection means 11. More specifically, the height information items for respective groups of the leads 2 on the respective lateral surfaces of the semiconductor device 1 are respectively input into the divided components 13a-13d of the storage device 13. The lead flatness detection means 15 receives the height information items 12 concerning the respective groups of the leads 2, which information items 12 are output from the storage means 13, so as to detect the maximum height among the height information items 12 as the lead flatness.
The lead flatness measurement apparatus described above presents the following problems. The mounting base 3 is rotated at low speed in order to avoid the displacement of the semiconductor device 1. It thus requires a long time to measure the flatness of all the leads of the semiconductor device 1. Further, if an imaging device is arranged on each lateral surface having the leads 2 of the semiconductor 1 projecting therefrom, it intervenes with the automatic feeding of the semiconductor device 1. Since the leads 2 are tilted, the first and second imaging devices 7a and 7b unfavorably forming images of the end surfaces 2a of the different leads 2, thereby lowering measurement accuracy. Moreover, since the measurement apparatus does not recognize the bottom surface of the package 1a of the semiconductor device 1, it is unable to measure the stand-off characteristics and the lead length of the semiconductor device 1. Additionally, it is impossible to carry out measurements if foreign matter adheres to the transparent mounting plate 4, or if the mounting plate 4 is scratched.